LLDP supports a set of attributes that it uses to discover neighboring devices. These attributes contain type, length, and value descriptions and are referred to as TLVs. LLDP frames are sent by each device on each port at a fixed frequency. A frame contains a Link Layer Discovery Protocol Data Unit (LLDPDU) which is a set of type-length-value (TLV) structures. LLDP supported devices use TLVs to send to and receive information from their immediate neighbors.

The LLDP frame starts with the following mandatory TLVs:

  • Chassis ID

  • Port ID

  • Time to live (TTL)

    The LLDP frame ends with a special TLV named “End of LLDPDU”. Refer the IEEE 802.1AB specification for a description of all the TLV types.

    Information that may be retrieved includes:

  • System name and description

  • Port name and description

  • VLAN ID

  • IP management address

  • System capabilities (switching, routing, and so on)

  • MAC/PHY information

  • Link aggregation